Without limiting the scope of the invention, its background is described in connection with methods to produce stable submicron peptide and protein particles.
For example, the U.S. Pat. No. 6,723,347 teaches a process for producing protein powder. The '347 patent describes a process for conveniently producing a stable protein powder retaining the higher-order structure at a high level which comprises freezing a protein-containing solution at a cooling rate of about −300 to −10° C./min. and then drying.
Another example can be found in U.S. Pat. No. 6,284,282, in which Maa et al. teach a method of spray freeze drying proteins for pharmaceutical administration. Maa's application relates to the spray freeze dry preparation of dry powder formulations of therapeutic proteins suitable for administration via pulmonary delivery.
Yet another example is found in U.S. Pat. No. 6,862,890 entitled “Process for Production of Nanoparticles and Microparticles by Spray Freezing into Liquid”. The '890 patent provides a system and a method for the production of microparticles and nanoparticles of materials that can be dissolved. The system and method provide quicker freezing times, which in turn produces a more uniform distribution of particle sizes, smaller particles, particles with increased porosity and a more intimate mixing of the particle components. The system and method of the '890 patent also produce particles with greater surface area than conventional methods, and a method for the preparation of particles. An effective ingredient is mixed with water, one or more solvents, or a combination thereof, and the resulting mixture is sprayed through an insulating nozzle located at or below the level of a cryogenic liquid. The spray generates frozen particles.
Yet another example is shown in the U.S. Pat. No. 6,254,854 by Edwards et al. entitled “Porous particles for deep lung delivery”. The '854 patent teaches improved porous particles for drug delivery to the pulmonary system, and methods for their synthesis and administration. The porous particles are made of a biodegradable material and have a mass density less than 0.4 g/cm3. The particles may be formed of biodegradable materials such as biodegradable polymers. For example, the particles may be formed of a functionalized polyester graft copolymer consisting of a linear a hydroxy-acid polyester backbone having at least one amino acid group incorporated therein and at least one poly(amino acid) side chain extending from an amino acid group in the polyester backbone. Porous particles having a relatively large mean diameter, for example greater than 5 μm, can be used for enhanced delivery of a therapeutic agent to the alveolar region of the lung. The porous particles incorporating a therapeutic agent may be effectively aerosolized for administration to the respiratory tract to permit systemic or local delivery of wide variety of therapeutic agents.
Finally, U.S. Pat. No. 5,019,400 teaches a very low temperature casting of controlled release microspheres The '400 patent describes a process for preparing microspheres using very cold temperatures to freeze polymer-biologically active agent mixtures into polymeric microspheres with very high retention of biological activity and material. Polymer is dissolved in a solvent together with an active agent that can be either dissolved in the solvent or dispersed in the solvent in the form of microparticles. The polymer/active agent mixture is atomized into a vessel containing a liquid non-solvent, alone or frozen and overlayed with a liquified gas, at a temperature below the freezing point of the polymer/active agent solution. The cold liquified gas or liquid immediately freezes the polymer droplets. As the droplets and non-solvent for the polymer is warmed, the solvent in the droplets thaws and is extracted into the non-solvent, resulting in hardened microspheres.
A disadvantage of the above mentioned techniques when used with proteins and peptides is that it that proteins and peptides often form aggregates when the particle size becomes smaller than about 1 μm, because they are exposed to large vapor-liquid interfaces during water removal. These aggregates remain upon reconstitution in buffer. Therefore, such techniques may not lead to biologically active micronized protein powders.
Furthermore, it is difficult to control the particle size distribution in these processes in many cases. Methods are needed to remove water from solutions of peptides and proteins to produce small particles, with control of the size distribution, without forming protein aggregates.